Genetic analyses of atypical Toxoplasma gondii strains reveal a fourth clonal lineage in North America

Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
International journal for parasitology (Impact Factor: 3.87). 02/2011; 41(6):645-55. DOI: 10.1016/j.ijpara.2011.01.005
Source: PubMed


Toxoplasma gondii is a widespread parasite of animals that causes zoonotic infections in humans. Previous studies have revealed a strongly clonal population structure in North America and Europe, while strains from South America are genetically separate and more diverse. However, the composition within North America has been questioned by recent descriptions of genetically more variable strains from this region. Here, we examined an expanded set of isolates using sequenced-based phylogenetic and population analyses to re-evaluate the population structure of T. gondii in North America. Our findings reveal that isolates previously defined by atypical restriction fragment length polymorphism patterns fall into two discrete groups. In one case, these new isolates represent variants of an existing lineage, from which they differ only by minor mutational drift. However, in the second case, it is evident that these isolates define a completely new lineage that is common in North America. Support for this new lineage was based on phylogeny, principle components analysis, STRUCTURE analyses, and statistical analysis of gene flow between groups. This new group, referred to as haplogroup 12, contains divergent genotypes previously referred to as A and X, isolated from sea otters. Consistent with this, group 12 was found primarily in wild animals, as well as occasionally in humans. This new lineage also has a highly clonal population structure. Analysis of the inheritance of multilocus genotypes revealed that different strains within group 12 are the products of a single recombination event between type 2 and a unique parental lineage. Collectively, the archetypal type 2 has been associated with clonal expansion of a small number of lineages in the North, as a consequence of separate but infrequent genetic crosses with several different parental lines.

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    • "Strain ID ToxoDB PCR-RFLP Genotype # Genetic markers SAG1 (5′+3′) SAG2 alt. SAG2 SAG3 BTUB GRA6 c22-8 c29-2 L358 PK1 Apico GT-1 #10 (Type I) I I I I I I I I I I I PTG #1 (Type II) II II II II II II II II II II II CTG #2 (Type III) II or III III III III III III III III III III III MAS #17 u-1 I II III III III u-1 I I III I TgCgCa1 #66 I II II III II II II u-1 I u-2 I TgCtBr5 #19 I III III III III III I I I u-1 I TgCtBr64 #111 I I u-1 III III III u-1 I III III I TgRsCr1 #52 u-1 I II III I III u-2 I I III I Present study TgMooseUS1 #5 u-1 II II II II II II II I II I TgMooseUS2 #7 I III III III III III III III III III I TgMooseUS3 Possibly new type u-1 II II II II III III II ND III ND ND data not available Table 1 Bioassay and isolation of Toxoplasma gondii from moose myocardium from northeastern Minnesota, USA Moose Toxoplasma gondii ID Gender Age Presumed cause of death MAT titer Mouse bioassay Strain designation SW KO 168 Female 8 years Capture-related >200 3/3 a 1/1 TgMooseUS1 53114 Female 1 year Hit by car <25 2/2 0/0 TgMooseUS2 13260 Male 20.5 days Bear attack <25 2/2 0/0 TgMooseUS3 SW Swiss Webster, KO interferon gamma gene knockout a No. of mice T. gondii positive/no. of mice inoculated Parasitol Res consequences (Dubey et al. 2011; Khan et al. 2011; VanWormer et al. 2014 "
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    • "These genotypes were deposited into the public database in ToxoDB and therefore designated as ToxoDB PCR-RFLP genotypes. Among these genotypes , a fourth clonal lineage (Type 12, its designation derived from haplogroup 12) in North America was recently recognized (Khan et al. 2011). This lineage consists of ToxoDB genotypes #4 and #5 (Shwab et al. 2014). "
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